1. Field of the Invention
The present invention relates to a developer quantity control blade and an image forming apparatus for use in electrophotographic image formation.
2. Description of the Related Art
In electrophotographic image formation, a developer quantity control blade is used as a unit that controls the thickness of a layer of a developer (hereinafter, also referred to as “toner”) so as to make it thin, and here, the developer is born by a developer bearing member and conveyed thereby to an image bearing member. The developer quantity control blade abuts with the developer bearing member to allow the toner to pass through a space between abutment portions, thereby controlling the thickness of the toner layer. A method is also known which includes forming a thin layer of the toner on the developer bearing member and also providing frictional electrification (tribo) that is for developing a latent image to the toner by friction at the abutment portion.
The toner has been recently reduced in particle size in order to achieve an increase in image quality, and therefore the toner may be conveyed to the image bearing member without being sufficiently brought into contact with the developer quantity control blade and the developer bearing member, which causes an insufficient charge of the toner to result in an insufficient image density.
As the method that solves such a problem, a method is considered which includes increasing the abutting pressure of the developer quantity control blade with the developer bearing member to allow the toner to be strongly pushed onto the developer bearing member. In this method, however, the thickness of the toner layer on the developer bearing member may be difficult to sufficiently ensure, and also the toner may be fixed to a nip portion in an abutting region of the developer bearing member with the developer quantity control blade to thereby cause streak-like unevenness in an image.
Japanese Patent Application Laid-Open No. 2007-293093 discloses a method which includes applying a voltage to a developer quantity control blade to thereby generate a difference in potential between a developer bearing member and the developer quantity control blade in order to perform active charge injection to toner. With respect to the method in Japanese Patent Application Laid-Open No. 2007-293093, however, the blade member is configured by a material including a block copolymer having a polyether structure and an ion conductive agent, and it has been found according to studies by the present inventors that the block copolymer and the ion conductive agent may bleed from the blade member to contaminate the developer bearing member to thereby cause horizontal streaks in an image.
In view of bleeding of the material from the blade member, Japanese Patent Application Laid-Open No. 2001-356594 discloses a developer quantity control blade including a polyurethane elastomer produced from a polyol component and a polyisocyanate component as main raw materials, in which the content of a component to be extracted with acetone as a solvent is 10% by mass or less. According to studies by the present inventors, the developer quantity control blade in Japanese Patent Application Laid-Open No. 2001-356594 effectively suppresses bleeding of the material from the blade member; however, it includes no conductive agent, and thus is difficult to apply to the method proposed in Japanese Patent Application Laid-Open No. 2007-293093, which includes applying a voltage to a developer quantity control blade for charge injection to toner.
The present invention is directed to providing a developer quantity control blade that can sufficiently impart charge to toner by application of a voltage to the developer quantity control blade and that allows contamination of a developer bearing member due to bleeding of a material from a blade member to be suppressed.
The present invention is also directed to providing an image forming apparatus that serves for stable formation of a high-quality electrophotographic image.